This invention relates to a method and apparatus for producing metallic rings which are, for example, employed to fabricate starting ring gears for a motor vehicle or the like, in particular, to a method and apparatus for producing annular metallic blanks for the metallic rings above.
There are two conventional methods for producing steel rings which are employed to fabricate ring gears or the like.
In one of the conventional methods for producing steel rings, an elongated steel material such as steel bar is bent into an annular shape and, then, the opposite ends of such formed steel material are joined together by a welding operation. However, according to that method, when the steel material is bent into annular shape, the ends of the material are left unformed or straight because the ends are held by gripping means while the material is being bent. Thus, when the ends of the annular material are welded together, the straight ends have to be cut off; then the ends of the remaining material which has been bent to a predetermined curvature are welded together. The cut off ends are waste. Furthermore, the ends formed by cutting off the straight part of the annular material are separated from each other and have to be butted against each other before they are welded together. The butting operation, however, results in application of an excess amount of stress to the material which may cause deformation of the material into oval or the like shape other than a true circle. In order to check and rectify the deviation from the desired true circle shape, further labor is required and checking and rectifying operation adds an additional cost to the production of the rings. Furthermore, since any steel material generally has a variation or deviation in carbon content therein over the length of the material, various positions of the steel material will have somewhat different curvatures and rectifying operation of such different curvatures will also require additional labor and expense.
In the second conventional method, a thick steel cylinder is sliced into a plurality of rings, the diameter of the steel cylinder having a predetermined diameter the same as that of the desired ring products so that the rings formed are, themselves, used as ring products.
In this method, however, a substantial amount of material is washed as cutting chips when the steel cylinder is sliced, thus resulting in increased production costs. Furthermore, the obtained rings are subjected to uneven stress while they are being cut from the steel cylinder and in consequence, the configuration of the obtained rings will come to be distorted even if the steel cylinder has a relatively precise circular configuration. Such distortion of configuration has to be corrected or rectified and, as with the first conventional method described above, this requires a substantial increase in man hours and expenditure.
With the above disadvantages of the prior art above in mind, the applicant previously invented a new method and apparatus and disclosed them in Japanese Pat. application No. 29353/1975 filed on Mar. 11, 1975, entitled "A Method and Apparatus for Making Annular Metallic Blanks for Metallic Rings". According to the invention disclosed in the Japanese Application above, a length of elongated metallic material, such as steel bar having a predetermined or desired cross-section configuration, is formed into a spiral member having a diameter smaller than that desired for rings to be formed, the spiral member is forcibly coaxially disposed around or put on a cylindrical portion of a holding means which has a diameter greater than that of the desired ring, and then, the spiral member is cut along a straight line parallel to the axis of the cylindrical portion to provide a plurality of bends. Thereafter, such bends are removed from the cylindrical portion to obtain annular blanks for rings.
In order to obtain a desired ring from the annular blank formed in accordance with the invention as described above, the ends of the annular blank are brought together in an abutting relationship and are joined together by a welding operation.
According to the invention described above, since a preformed spiral member is forcibly disposed about the cylindrical portion having an outer diameter greater than that of the spiral member, deviation or variation in curvature in several portions of the spiral member which may be inevitable when the spiral member is formed by merely bending the metallic material such as steel bar, for instance, due to variation in carbon content with respect to the length of the material, can be rectified, and, thus, the deviation or variation in curvature of the annular blanks made from such a spiral member can be eliminated. Accordingly, the rings made from such annular blanks have substantially no the deviation or variation in curvature thereof and the invention can solve the difficulty inherent in the first conventional method as described hereinabove. Furthermore, the ends of the annular blanks produced as described above remain in an abutting relationship so little or no external force needs to be applied to position them for welding. The invention makes it easy to produce rings having a desired diameter without substantial variation in the radius of curvature.
Furthermore, the material loss in the above-mentioned invention is small in comparison with that of the first and second prior art methods described above.
However, it was found that the invention has the disadvantage as described below. That is in coaxially disposing the spiral member about the cylindrical portion, each of turns of the spiral member disposed around the cylindrical portion is caused with circumferencial relative movement with respect to the adjacent turns so as to conform to the cylindrical portion having the diameter larger than that of the spiral member and, thus, a substantial amount of frictional force is generated between the adjacent convolutions or turns of the spiral member as well as between the spiral member and the cylindrical portion. Therefore, it is necessary to apply a substantial pressure on one end face of the spiral member in the axial direction thereof in order to push the spiral member to the predetermined position about the cylindrical portion along the axial direction of cylindrical portion. Further, such a great axial pressure, in turn, increases the frictional force between the turns so that the circumferential relative motion of each turn of the spiral member as described above cannot be freely effected. However, when such turns are forcibly pushed around the cylindrical portion, the turns are subjected to plastic deformation which causes inconvenience in the subsequent working process. Furthermore, it is difficult to uniformly effect the operation for forcibly disposing the spiral member about the cylindrical portion.